Flat cables are used with various structures. A frequent use is an insulated double conductor, with both conductors or wires mechanically connected through their insulation and a web there between. In cross-section such a double wire forms an eight. It is also known to provide one wire with a smaller diameter than the other. In these or similar flat cables the smaller side in cross-section is circular or elliptical. It is further known to provide a flat cable with a rectangular cross-section with non-rounded, circularly or elliptically rounded edges or corners.
Sector cables are single wires for multiple wire cables and usually have a sector angle of 90° or 120°. The outer side of the sector cable is circular in cross-section, and the sides which intersect in the centre of the circle are rounded in the section area. Thus, two opposed circular sections exist, having different radii.
It is a necessity to control the dimensions of such profiles during manufacture in order to achieve constant desired sizes or dimensions. It is known to illuminate articles of the kind mentioned transverse to their longitudinal axis, preferably by parallel rays and to determine the shadow borders on a light sensitive sensor. In this method, it is necessary to precisely lead the articles with respect to their angular position. A certain rotation about the longitudinal axis results in failures of the measurement values. It is further disadvantageous that the generation of parallel rays by means of a collimator or the like results in measurement failures for inaccuracies of the optical system used. If an orthogonal measurement along two orthogonal axes is carried out, the danger exists that the sensor or the light source beneath the article suffers from contamination.
In this connection, it has been further become known to rotate the article about the longitudinal axis in an oscillating manner and to determine the minimum and the maximum values. This method leads to improved measurement values, however, necessitates a continuous partial rotation of the article.
From DE 197 57 067 C2 a method for measuring the diameter of thin cables has become known wherein the cable is illuminated by a fan-shaped beam of a monochromatic point-shaped light source in a measuring plane, with the main beam direction being approximately perpendicular to the axis of the cable. The light is received by means of a light sensitive line sensor on the opposite side of the cable with the axis of the sensor approximately being perpendicular to the main beam direction. The diameter of the cable is determined by evaluating the intensity curves of the diffraction pattern at the edges of the shadow caused by the article under consideration of the measured distance between the article and the sensor.
It is an object of the invention to provide a method to determine a dimension of an article, in particular of a flat cable or a sector cable, which independent of the rotational position of the article allows a relatively precise measurement.